Research Of Self-tracking Log-domain Filter

The self-tracking filter can filter out all kinds of interference phase noise effectively in the process of signal transmission. The characteristics frequency of the circuit can track the change of carrier or fundamental automatically. Thus self-tracking filter has a high Q value and a high signal to noise ratio, and has important application value in the fields of electronic communication and measurement. Pointing at the current self-tracking filter’s low working frequency, narrow dynamic tuning range and high power consumption and other shortcomings, the thesis designs a new kind of analog self-tracking filter which fused frequency-tracking circuit and the log-domain filter together, and filtering frequency can track the input signal frequency quickly and automatically.The key research questions are as follows: to explore the design method of active power filter based on current-mode processing technology; making full use of current-mode circuit large dynamic range, high working speed and other advantages, to study and design a kind of log-domain filter which combined exponent extension, log-domain integrator unit with logarithmic compression; to study the implementation of superior performance broadband frequency-current conversion circuit which uses AD650 and OP37, to break the bottleneck of narrow frequency range and slow processing speed of general F/I circuit, to realize the high frequency self-tracking filtering.The major of the thesis is summarized as follow:(1) After reading a large number of references at home and abroad, this thesis introduces the development trend, applications and research status of self-tracking filter, and summarizes and compares existing analog self-tracking filter design methods, proposing a high-performance broadband frequency-current conversion(F/I) circuit using AD650 and OP37, combining log-domain filters to achieve the filtering frequency quickly and automatically adapt to the design of analog filters to be processing the signal frequency changes.(2) The thesis details the basic concepts and characteristics of current-mode circuits, and the working principle of current mirror circuit; the thesis also introduces the basic principles and sub-module unit of log-domain filters, and its incomparable advantages and characteristics compared with conventional filter.(3) The design achieves signal preprocessing amplifier circuit and V/I circuit; design the frequency self-tracking circuit including two-way limiter circuit, shaping circuit and broadband frequency-current conversion circuit, for the signal frequency tracking. And to a part of the circuits by the simulation and actual circuit measurement.(4) By using transistors and a small amount of resistors and capacitors, we achieved log-domain filter circuit. And a variety of log-domain filter circuit designs are analyzed theoretically and pass the ORCAD simulation software’s examination, part of the circuits are experimental measured.The filtering frequency of the self-tracking log-domain filter proposed in this thesis can track the changes of the input signal frequency and automatic updates and dynamic adjustment. It has advantages of wide range of filtering frequency, simple circuit structure, easy tuning, etc., can be widely applied to various fields in the data processing, breaking the obstacle of the signal to be processed changing in large frequency range.